This invention relates generally to conversion of the forces of fluid flowing under pressure into rotary motion, the speed and torque of which are infinitely variable. More particularly, but not exclusively, this invention relates to hydrostatic power transmission in which fluid under pressure is received from a source, such as a closed-center type of hydraulic system, a pilot controlled variable displacement fluid motor, in which the motor output direction and speed is responsive to the relative rotational direction and speed of a control element, and wherein torque output capability is automatically adjusted to torque demand. The invention is particularly adaptable to power transmission applications in which precise but variable control of speed and torque is desired. For example, heavy duty machinery has requirements for such power transmission systems for operating cable winches, propelling vehicles and driving rotating components.
Hydrostatic motors having integral speed reduction/torque multiplying characteristics in the area of medium to light duty are frequently adapted for powering various mechanisms which may be located remotely from a power source. Such devices may be of the fixed displacement type and include orbital movement reduction gearing. An example of a motor of this type, which also includes a cylinder block having a radial piston configuration, is disclosed in U.S. Pat. No. 3,339,460. This type of motor has no provision for varying the piston displacement for the purpose of altering the direction of rotation or the speed and torque output. The direction of rotation is sometimes controlled by a manually operated 4-way valve. In some hydrostatic power applications it is the practice to use a variable displacement, reversible flow pump as the fluid pressure source, and to control the pump flow output in such a manner as to provide a corresponding direction of motor rotation and speed output. Since such a motor is of the fixed displacement type, the torque output capability is constant. A low torque requirement for a given speed setting results in a reduced fluid pressure volume being delivered by the pump, thereby eliminating the fluid pressure source for possible use in performing other functions.
Other hydrostatic motors are of the variable displacement type in which a control may be adjusted to a specific speed and torque capability setting. The fluid pressure source may be either a fixed displacement or a variable displacement pump. In the case of the latter, the usual practice is to mechanically coordinate the pump and motor controls. In the case of the former, the pump pressure varies according to the torque demand on the motor at any given speed setting; sometimes, relatively complex flow control and sequence valves are used in an attempt to control hydraulic conditions within the system. It is apparent, therefore, that in any of the prior art referred to, the fluid pressure source is primarily limited to a single function.
In view of the need for improved fluid motors, transmissions and controls, it is an object of the invention to provide an improved fluid motor and drive unit.
It is another object of this invention to provide a fluid motor having a configuration which uses fluid from a closed-center type or other fluid pressure source at a predetermined pressure level.
Another object is to provide a fluid motor which has integral gear reduction for use in applications wherein the driven member is a low speed, high torque member.
A further object is to provide a variable displacement fluid motor having pilot or follow-up control in which motor speed output is responsive to control speed input and wherein torque output is automatically adjusted to torque demand.
It is another object to provide an improved fluid motor in which static, dynamic, and pressure balance is achieved under all contemplated operating conditions to a substantial degree.
Still another object of this invention is to provide a fluid motor adaptable to various modes of control input.
It is a further object to provide a fluid motor having commonality of component parts thereby favorably influencing production and service costs.
Still another object is to provide a fluid motor which includes a control member which is movable between a plurality of positions and which, during movement between said positions, acts to vary the output torque and/or direction of the motor drive.
A still further object is to provide a fluid motor, transmission, and speed and torque control unit contained in a single housing.
Another object is to provide a fluid motor having means for varying the stroke of the pistons during operation so as to control the torque output of the motor, and having an operative connection between the power output member and the stroke control mechanism.
Another object is to provide a hydraulic motor and drive unit having improved fluid flow control means including means for insuring relatively smooth, shock-free operation of the motor even when the motor is operated under high fluid pressure.
Another object is to provide a fluid motor and transmission which is particularly adapted to operation in a closed loop or servomechanism mode of operation.
A still further object is to provide a motor and variable speed drive which is capable of delivering significant power but which is very compact in size.
These and other objects are attained in accordance with the present invention wherein there is provided a pilot controlled variable displacement fluid motor of the reciprocating piston type having a cylinder block co-axially and rotatably associated with relation to a motor frame which is rotatable to its support housing. Planetary or other reduction gearing drivingly joins the cylinder block, the motor frame, and the support housing, for maintaining a predetermined rotational relationship therebetween. The integral planetary gearing provides a torque multiplication between the cylinder block, which is the driving element, and the motor frame, which is the motor output or driven element. The planetary gearing system adapts the motor to accommodate a follow-up type of pilot control mechanism. The pilot control mechanism includes portions which are rotatably associated with the motor frame and the mechanism is adjustable for controlling the direction of rotation, the speed, and the torque output, of the motor by varying the piston stroke, or displacement, in response to a desired speed control input and a torque output demand upon receiving fluid from a fluid pressure source at a predetermined, substantially constant pressure level, such as from a closed-center type hydraulic system.
Further objects of the invention, together with additional features contributing thereto, the advantages accruing therefrom, and the manner in which they are attained, will become more apparent from the following detailed description of a preferred embodiment of the invention set forth by way of example and shown in the accompanying drawings wherein like numerals indicate corresponding parts throughout wherein: